Custody out of state (last time)

My ex and I have joint legal custody of our 2 children. I have primary placement. We have an order of visitation and 4 months after our divorce he wen to his girlfriends house in Arizona for the winter and expected me to change the summer visitation to accommodate him. After a 2yrs fighting with him over the divorce I couldn't fight any longer and I agreed. That was this past summer.
November 25th he left again for Arizona. He hasn't been back to Wisconsin since. I haven't recieved a call from him since he left, in fact he never told me he was leaving he just disappeared. He has talked to the children on their cell phones and does let them know briefly what he is doing.
He called me on January 9th and asked if the kids could come to AZ to visit hum during their winter break. I told him we already had plans but I would talk it over with my husband and see if we could make arrangements. When I called him back and said we would cancel our vacation and let the kids visit, I gave him the dates the kids would be out of school. He wasn't happy with 6 days! He wanted 8 to make it worth his while spending $700 on plane tickets. Keep in mind he is 2 mos in arrears for child support and owes me $400 in medical bills.
I explained to him that our daughter is not doing well in school and she souldn't be missing any at this time and the fact they have sports.. wrestling, tae kwon do, dance and girl scouts.
He said, See you in COURT
He did the same thing last year when he went to AZ and claimed to the judge that he had already purchased plane tickets... Which he Didn't! They Drove!
My question is.. Am I being unreasonable?? Do I have to let them go on "his terms" and will he win in court?

That behavior is not reasonable and you will very likely prevail in court; the children do need stability and education time etc. as a crucial priority.